With the rapid development of optical communications technologies, implementation of the dense wavelength division multiplexing technology (Dense Wavelength Division Multiplexing, DWDM) greatly improves the capacity and transmission distance of an optical fiber communications system, and from a sending end to a receiving end, each wavelength signal needs to pass through filter devices, such as a multiplex, a comb filter, and a demultiplexer. On the other hand, an optical network structure evolves from a ring network to a mesh network, and massive optical filters will be used on a network to process a wavelength service.
With the increase of a signal modulation rate, width of a signal spectrum also becomes broader. On a high-rate system, such as 40 G and 100 G, performance of an optical fiber link is influenced when an optical filter filters a wavelength service, where influences mainly include two aspects: One aspect is as follows: On a system without an optical fiber, an optical signal to noise ratio (Optical Signal to Noise Ratio, OSNR) penalty, called a linear impairment, is generated because an optical filter cuts off a spectrum, and the linear impairment keeps unchanged in a situation that the number of optical filters is fixed and the number of signal spectrums is fixed, so that it is easy to establish a simple look-up table through a laboratory measurement. The other aspect is as follows: On a system with an optical fiber, in a situation that incident optical power is relatively high, an optical filter effect and a nonlinear effect work together and cause a nonlinear impairment to a signal, where an effect of the impairment cannot be ignored, and a size of a caused impairment is different if the number of optical filters is different or a location in which an optical filter is arranged in an optical fiber link is different.
The nonlinear schrodinger equation is a fundamental equation for studying transmission of an optical pulse in an optical fiber, and it is a scalar approximation form of a wave equation that is capable of explaining absorption, dispersion, and nonlinearity. Currently, the most conventional method for calculating a nonlinear transmission impairment of an optical fiber link having an optical filter is: solving the nonlinear schrodinger equation by using a numerical method and performing simulation for transmission of an optical signal in the link, so as to obtain the nonlinear transmission impairment, which is caused by various factors including the optical filter, of the optical fiber link. Currently, there are various methods for solving the nonlinear schrodinger equation for a quick numerical solution, such as the distribution Fourier method.
However, an analytical solution cannot be obtained from the nonlinear schrodinger equation. Therefore, it requires at least several hours to accurately calculate a nonlinear impairment of a long-distance optical fiber link even by using a professional server, and occupation of massive computer resources is required. Such calculating speed cannot be tolerated in a scenario requiring a rapid calculation, such as live network deployment, expansion, and maintenance.